Document how to configure and run load tests.

etc/load-testing/README.md

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+# `stackage-server` load tests
+
+This directory can be used to test an on-premises instance of `stackage-server` for quality of service metrics. Follow the instructions below to run it.
+
+We assume you will be using `pyenv` to handle different Python environments in a safe manner. If you prefer installing packages globally (not recommended), jump straight to the line commented with `# install dependencies`. Before doing anything, set an environment variable `STACKAGE_SERVER_REPO` on your shell to this repo’s root folder. Then copy everything and run:
+
+```shell
+cd ~
+curl -L https://raw.githubusercontent.com/pyenv/pyenv-installer/master/bin/pyenv-installer | bash
+
+# add the following lines to your shell initialisation for permanent usage
+export PYENV_VIRTUALENV_DISABLE_PROMPT=1
+eval "$(pyenv init -)"
+eval "$(pyenv virtualenv-init -)"
+
+# create an environment for tests
+pyenv install 3.6.3
+pyenv virtualenv 3.6.3 stackage-server-py-3.6.3
+cd "${STACKAGE_SERVER_REPO}/etc/load-testing"
+pyenv local stackage-server-py-3.6.3
+pyenv activate stackage-server-py-3.6.3 # should happen automatically on previous line, but just to be sure
+
+# install dependencies
+pip install -r requirements.txt
+
+# execute load tests
+locust --host="http://yourlocalinstance.domain"
+```
+
+Then navigate to [127.0.0.1:8089](http://127.0.0.1:8089), set the number of clients to simulate, spawn rate, start it and wait a few minutes for the results to stabilise. You can then download or analyse directly on Locust’s UI.